What Are the Different Types of Epilepsy?

Reviewed on 8/6/2018

Ask the Experts

My cousin started having seizures a month ago, and he's been to see a couple different neurologists. They still haven't been able to determine the root cause of his seizures. What could be the problems? What are the different types of epilepsy?

Doctor’s Response

Epilepsy is a disorder with many possible causes. Anything that disturbs the
normal pattern of neuron activity -- from illness to brain damage to abnormal
brain development -- can lead to seizures.

Epilepsy may develop because of an abnormality in brain wiring, an imbalance
of nerve signaling chemicals called neurotransmitters, or some combination of
these factors. Researchers believe that some people with epilepsy have an
abnormally high level of excitatory neurotransmitters that increase neuronal
activity, while others have an abnormally low level of inhibitory
neurotransmitters that decrease neuronal activity in the brain. Either situation
can result in too much neuronal activity and cause epilepsy. One of the
most-studied neurotransmitters that plays a role in epilepsy is GABA, or
gamma-aminobutyric acid, which is an inhibitory neurotransmitter. Research on
GABA has led to drugs that
alter the amount of this neurotransmitter in the brain or change how the brain
responds to it. Researchers also are studying excitatory neurotransmitters such
as glutamate.

In some cases, the brain's attempts to repair itself after a head injury, stroke,
or other problem may inadvertently generate abnormal nerve connections that lead
to epilepsy. Abnormalities in brain wiring that occur during brain development
also may disturb neuronal activity and lead to epilepsy.

Research has shown that the cell membrane that surrounds each neuron plays an
important role in epilepsy. Cell membranes are crucial for a neuron to generate
electrical impulses. For this reason, researchers are studying details of the
membrane structure, how molecules move in and out of membranes, and how the cell
nourishes and repairs the membrane. A disruption in any of these processes may
lead to epilepsy. Studies in animals have shown that, because the brain
continually adapts to changes in stimuli, a small change in neuronal activity,
if repeated, may eventually lead to full-blown epilepsy. Researchers are
investigating whether this phenomenon, called kindling, may also occur in
humans.

In some cases, epilepsy may result from changes in non-neuronal brain cells
called glia. These cells regulate concentrations of chemicals in the brain that
can affect neuronal signaling.

About half of all seizures have no known cause. However, in other cases, the
seizures are clearly linked to infection, trauma,
or other identifiable problems.

Genetic Factors

Research suggests that genetic abnormalities may be some of the most
important factors contributing to epilepsy. Some types of epilepsy have been
traced to an abnormality in a specific gene. Many other types of epilepsy tend
to run in families, which suggests that genes influence epilepsy. Some
researchers estimate that more than 500 genes could play a role in this
disorder. However, it is increasingly clear that, for many forms of epilepsy,
genetic abnormalities play only a partial role, perhaps by increasing a person's
susceptibility to seizures that are triggered by an environmental factor.

Several types of epilepsy have now been linked to defective genes for ion
channels, the "gates" that control the flow of ions in and out of cells and
regulate neuron signaling. Another gene, which is missing in people with
progressive myoclonus epilepsy, codes for a protein called cystatin B. This
protein regulates enzymes that break down other proteins. Another gene, which is
altered in a severe form of epilepsy called LaFora's disease, has been linked to
a gene that helps to break down carbohydrates.

While abnormal genes sometimes cause epilepsy, they also may influence the
disorder in subtler ways. For example, one study showed that many people with
epilepsy have an abnormally active version of a gene that increases resistance
to drugs. This may help explain why anticonvulsant drugs do not work for some
people. Genes also may control other aspects of the body's response to
medications and each person's susceptibility to seizures, or seizure threshold.
Abnormalities in the genes that control neuronal migration, a critical step in
brain development, can lead to areas of misplaced or abnormally formed neurons,
or dysplasia, in the brain that can cause epilepsy. In some cases, genes may
contribute to development of epilepsy even in people with no family history of
the disorder. These people may have a newly developed abnormality, or mutation,
in an epilepsy-related gene.

Other Disorders

In many cases, epilepsy develops as a result of brain damage from other
disorders. For example, brain tumors, alcoholism, and Alzheimer's
disease frequently lead to epilepsy because they alter the normal workings
of the brain. Strokes, heart attacks, and other conditions that deprive the
brain of oxygen also can cause epilepsy in some cases. About 32 percent of all
cases of newly developed epilepsy in elderly people appears to be due to
cerebrovascular disease, which reduces the supply of oxygen to brain cells. Meningitis, AIDS,
viral encephalitis, and other infectious diseases can lead to epilepsy, as can hydrocephalus --
a condition in which excess fluid builds up in the brain. Epilepsy also can
result from intolerance to wheat gluten (also known as celiac
disease), or from a parasitic infection of the brain called
neurocysticercosis. Seizures may stop once these disorders are treated
successfully. However, the odds of becoming seizure-free after the primary
disorder is treated are uncertain and vary depending on the type of disorder,
the brain region that is affected, and how much brain damage occurred prior to
treatment.

Epilepsy is associated with a variety of developmental and metabolic
disorders, including cerebral
palsy, neurofibromatosis,
pyruvate dependency, tuberous sclerosis, Landau-Kleffner
syndrome, and autism.
Epilepsy is just one of a set of symptoms commonly found in people with these
disorders.

Head Injury

In some cases, head injury can lead to seizures or epilepsy. Safety measures
such as wearing seat belts in cars and using helmets when riding a motorcycle or
playing competitive sports can protect people from epilepsy and other problems
that result from head injury.

The developing brain is susceptible to many kinds of injury. Maternal
infections, poor nutrition,
and oxygen deficiencies are just some of the conditions that may take a toll on
the brain of a developing baby. These conditions may lead to cerebral palsy,
which often is associated with epilepsy, or they may cause epilepsy that is
unrelated to any other disorders. About 20 percent of seizures
in children are due to cerebral palsy or other neurological abnormalities.
Abnormalities in genes that control development also may contribute to epilepsy.
Advanced brain imaging has revealed that some cases of epilepsy that occur with
no obvious cause may be associated with areas of dysplasia in the brain that
probably develop before birth.

Poisoning

Seizures can result from exposure to lead, carbon monoxide, and many other
poisons. They also can result from exposure to street drugs and from overdoses
of antidepressants and
other medications.

Seizures are often triggered by factors such as lack of sleep,
alcohol consumption, stress,
or hormonal changes associated with the menstrual cycle. These seizure triggers
do not cause epilepsy but can provoke first seizures or cause breakthrough
seizures in people who otherwise experience good seizure control with their
medication. Sleep deprivation in particular is a universal and powerful trigger
of seizures. For this reason, people with epilepsy should make sure to get
enough sleep and should try to stay on a regular sleep schedule as much as
possible. For some people, light flashing at a certain speed or the flicker of a
computer monitor can trigger a seizure; this problem is called photosensitive
epilepsy. Smoking cigarettes
also can trigger seizures. The nicotine in
cigarettes acts on receptors for the excitatory neurotransmitter acetylcholine
in the brain, which increases neuronal firing. Seizures are not triggered by
sexual activity except in very rare instances.